The rolling bearing is provided with a seal or a shield member (also called as “seal material” hereafter) on a bearing ring for avoiding leakage of a sealed grease, a lubricant or invasion of foreign materials from an outside. For example, a ball bearing shown with a cross section in FIG. 1 has a structure which rotatably holds, via a retainer 7a, plurality of balls 5 between an inner ring 2 having an inner ring raceway 1 and an outer ring 4 having an outer ring raceway 3, and further secures seal materials 6 to the outer ring 4. The seal material 6 employs a metal-made seal material by processing such as a steel sheet in a desired shape, and beside as shown in FIG. 2, it employs a rubber-made seal material as one-body of a steel-made core 6a and an elastic member 6b. 
Ordinarily, the seal material 6 is treated with corrosion resistance for avoiding corrosion by oxidation. For example, Japanese Patent Laid Open No. 62989/1999 describes, as schematically shown in FIG. 12 of the present specification, a product made by plating a Zn film 11 on a surface of a steel material 10, and on this Zn plated steel material, forming a chromate film 12 to protect the Zn film 11. In addition, another product is also known where, as schematically shown in FIG. 13 of the present specification, the steel material 10 is plated on the surface with the Zn film 11, and the chromate film 12 is formed on the Zn plated steel material to protect the Zn film 11, and further a protective film 13 of lithium silicate is provided thereon.
The above Zn plated steel material prevents the steel material 10 from corrosion by selectively ionizing a zinc being a metal which is electrochemically baser than the iron existing in the steel material 10, and this is the steel sheet of corrosion resistance being so-called self-sacrifice type. But, since the zinc is checked from elusion by the chromate film 12 formed on the Zn film 11, the corrosion resistance by the inherent self-sacrifice type is not enough displayed, and rusts are not enough checked. In case the rust appears on the raceway surface of the bearing, inconveniences such as acoustic failure or non-uniformity in torque are caused, and become fatal defects. Particularly, in the bearing sealed with the grease, the rust easily occurs on the raceway surface, and this is a big problem.
The chromate film 12 is usually formed by an electrolytic treatment of chromate (VI) solution, and the chromate (VI) elutes into a soil from wastes of the chromate treated parts, creating a serious environmental problem, and there is another problem that the forming of the chromate film 12 is not preferable from a viewpoint of an environmental protection.
Under these circumstances, the present invention has been made, and it is an object to offer such a rolling bearing excellent in the corrosion resistance and also suited to the environmental protection.